It definitely sounds like something is wrong with your battery Mrs_Often. I read for about 5 hours per day and charge every two weeks, whether I need to or not.

When I exchanged my Glo due to a faulty light button, I sent Kobo an email on a Saturday, and on the following Tuesday (1 week, 2 days) my replacement device was delivered. I think dealing with Kobo directly will be your best bet for a resolution. Good luck!